the window geometry settings are saved in ~/.kvirc/config/winproperties.kvc . Deleting that file you lose any window specific option (encoding for channels, windows geometry, docking status, ...). Instead, if you want to reset that value just for one/some channels: once you resize the userlist, right click on the channel name in the taskbar (channels list) and choose "save window properties".

Winrect: external geometry of the window (x, y, width, height);
TopSplitter: geometry of the top splitter (contains topicbar and "bans", "channel modes", "encoding", ... icons) (width, height)
Splitter: width of the ircview, width of the nicklist.
VertSplitter: heigth of the two ircview if using the "double view" feature